1. Field of the Invention
This invention relates to wireless sensing station for use in a wireless network for monitoring sensed physical conditions and more specifically to a modular, low-power architecture for a Wireless Integrated Network Sensor (WINS) Node.
2. Description of the Related Art
Sensor networks have numerous applications, such as security, industrial monitoring, military reconnaissance and biomedical monitoring. In many such applications it is either inconvenient or impossible to connect the sensors by wire or cable; a wireless network is preferable.
Wireless networks of sensor stations, however, present several technical challenges. Wireless communication generally requires higher power than wired communication over the same distance; but an individual wireless sensor station requires a limited, self-contained power supply, which usually dictates that it conserve energy. The resulting low power constraint severely limits the range of wireless transmission by an individual sensor station. If control or data processing occurs at a central location, then the entire network is vulnerable to failure of the central processor. For both power conservation and robustness, each sensor station should locally process the sensor data and make local decisions to reduce the amount of data transmitted and to distribute decision making.
U.S. Pat. No. 5,854,994 describes a wireless system for monitoring the health of a plurality of machines, such as in a manufacturing plant, consisting of a plurality of machine monitors mounted on a plurality of machine measuring points. Each machine monitor includes at least one sensor to sense a characteristic of the machine at the machine measuring point and generate at least one sensor signal. Each machine monitor also includes a data processor for receiving and analyzing the sensor signals, for producing analyzed signals based on the sensor signals, and for producing selected data based on the analyzed sensor signals. Each machine monitor contains a transmitter, which produces wireless transmission signals corresponding to the sensor signals, and a receiver. The apparatus also includes a command station with a receiver for receiving the transmission signals from the machine monitors and a transmitter for issuing commands to the machine monitors. The command station stores data corresponding to the received signals, which are representative of the sensed characteristic of the machine. To conserve power, a time in the machine monitor energizes and de-energizes the sensor, data processor, and transmitter at selected times.
The shortcomings of the '994 machine monitoring system are a hard-wired architecture that is not scalable and power cycling that is on a fixed schedule between on and off modes of operation.
U.S. Pat. No. 6,208,247 describes a sensing station that when deployed in a network allows monitoring of the spatial extent and distribution of a sensed condition that overcomes many of these limitations. The sensing is a miniature electronic sensing station, adaptable for two-way wireless communication in a network with other similar sensing devices, for sensing events such as an intrusion, vehicle movement, a change in status of some industrial process, or any physical change that can be detected by the sensors. As shown in FIG. 3 of the '247 patent, each sensing station includes one or more sensors connected to a WINS node. Each node includes a digital signal processor for analyzing the data from the sensors; a programmable microprocessor for making decisions based upon the analyzed data, and for controlling communication functions; a power supply; and a wireless transceiver that communicates using a synchronous multi-access such as Time Division Multiple Access (TDMA), code division multiple access (CDMA) or frequency division multiple access (FDMA), for communicating with other nodes in the network and with users all enclosed in a single package. The DSP is hard-wired to the microprocessor, which in turn is hard-wired to the wireless transceiver to optimize performance and cost of a particular design. Circuits which are not required to be active during a time window are held in an inactive “sleep mode” so as to conserve power.
The shortcomings of the '247 WINS node are that its hard-wired architecture is not modular hence not scaleable and is not flexible enough for optimum power management.